1. Field of the Invention
The present invention relates to a soft magnetic film comprising a FeNi alloy, and particularly to a soft magnetic film having both a high saturation magnetic flux density Bs and high corrosion resistance, a thin film magnetic head using the same, and a method of producing the soft magnetic film and a method of manufacturing the thin film magnetic head.
2. Description of the Related Art
A conventional soft magnetic film comprises a FeNi alloy having a Fe composition ratio of about 55% by mass and a Ni composition ratio of about 45% by mass, and having a saturation magnetic flux density Bs of about 1.6 T.
As shown in FIG. 1, such a soft magnetic film is used for a thin film magnetic head in which a recording head h2 comprises a lower core layer 7 and an upper core layer 10 each of which comprises a soft magnetic film, and which are opposed to each other with a coil layer 9 provided therebetween.
In the recording head h2, a recording magnetic field is induced in each of the upper core layer 10 and the lower core layer 7 by a coil current, and a recording signal is applied to a magnetic disk by a leakage magnetic field between the upper core layer 10 and the lower core layer 7. In order to increase the recording density, it is desirable to increase the saturation magnetic flux density Bs of the soft magnetic film which constitutes each of the upper core layer 10 and the lower core layer 7.
Although the saturation magnetic flux density of the soft magnetic film made of the FeNi alloy can be increased by increasing the Fe composition ratio, the soft magnetic film has a problem in which an increase in the Fe composition ratio deteriorates corrosion resistance.
Particularly, when the track of a thin film magnetic head is further narrowed accompanying increases in the recording density in the future, a pole layer having a high saturation magnetic flux density and excellent corrosion resistance must be formed in a very narrow region.
Therefore, the conventional NiFe alloy causes difficulties in manufacturing a thin film magnetic head adaptable to a higher recording density.